My U.S. Pat. No. 3,716,990 teaches a method of improving the efficiency of steam or other condensing vapor cycles. In general the method is to use the work of expansion of a given weight of steam at a given high entropy, to compress in a positive displacement compressor a greater weight of steam at a lower entropy. The total weight of steam is then heated to maximum operating pressure and temperature. One portion of the steam is expanded in a reciprocating expander-compressor as above; and the remainder is used for further useful work, by expansion, for example, through a turbine.
The favored method for the expansion-compression part of the cycle is a steam-operated free piston expander-compressor.
As taught in the reference patent, the cycle has the characteristic that the expansion and compression stages of the positive displacement expander-compressor must be matched by expansion of some steam through a turbine thus:
1. The positive displacement expander-compressor cannot be operated above the maximum turbine inlet pressure in an existing steam plant; and PA1 2. The theoretical advantage of using a positive displacement expander-compressor over a high pressure range is partially off-set by the relatively low efficiency of very high pressure turbines. PA1 a power producing method, of the external combustion type, including heating a condensable vapor to a predetermined temperature at a predetermined pressure: PA1 Expanding the heated condensable vapor in a first work producing zone to a lower pressure; PA1 Reheating the expanded vapor; PA1 Expanding the reheated vapor to a lower pressure in a second work producing zone; PA1 Passing a portion of the expanded vapor to a work- demanding zone; PA1 Condensing the remainder of the expanded vapor; PA1 Adding the condensate or its weight equivalent to the vapor in the work-demanding zone; PA1 Utilizing the work produced in expanding the vapor in the first work-producing zone to compress to the original predetermined pressure the vapor passed to the work-demanding zone, plus the added condensate from the vapor expanded to the lower pressure; and by PA1 A power producing method, of the external combustion type, including heating a condensable vapor to a predetermined temperature at a predetermined pressure; PA1 expanding the heated condensable vapor in a first work producing zone to lower pressure; PA1 reheating the expanded vapor; PA1 expanding the reheated vapor to a lower pressure in a second work producing zone, passing a portion of the expanded vapor to a work-demanding zone; PA1 expanding the remaining portion to a still lower pressure; PA1 condensing the expanded portion to liquid; PA1 adding the condensate from the portion of the vapor expanded to the lower pressure, to the vapor in the work-demanding zone; PA1 utilizing the work produced in expanding the vapor in the first work-producing zone to compress to the original predetermined pressure the vapor passed to the work-demanding zone, plus the added condensate from the vapor expanded to the lowest pressure.